1. Field of the Invention
The present invention relates to a remaining battery power calculation circuit.
2. Description of the Related Art
In portable electronic equipment such as a cellular phone, a digital camera and the like, generally, remaining power of a battery, which is used as a power source, is calculated and the remaining battery power is displayed. Methods of calculating the remaining battery power include a method of calculating the remaining battery power by detecting an output voltage of a battery and a method of calculating a remaining battery power by detecting a charging/discharging current of a battery, for example (See Japanese Patent Laid-Open Publication No. 2005-345172 and Japanese Patent Laid-Open Publication No. 2007-240523, for example).
In the method of calculating the remaining battery power based on an output voltage of a battery, a microcomputer or the like which detects an output voltage of a battery, for example, uniquely calculates the remaining battery power from the output voltage of the battery. However, the output voltage of the battery varies with a load current of a load connected to the battery, a change in internal resistance of the battery and the like. Thus, with the method of calculating the remaining battery power only from the output voltage of the battery, it is difficult to calculate the remaining battery power with accuracy. On the other hand, with the method of detecting remaining battery power based on a charging/discharging current of the battery, a microcomputer or the like, which detects a charging/discharging current of the battery, calculates remaining battery power by integrating the charging/discharging current, for example, and thus the remaining battery power can be calculated with accuracy. However, in order to detect the charging/discharging current, a resistor or the like, which detects the charging/discharging current, needs to be connected to the battery in series, which deteriorate efficiency as a power source. Further, since an AD (Analog to Digital) converter, a microcomputer or the like, which detects a charging/discharging current, needs to be provided in a battery pack, which leads to a problem that the battery pack becomes expensive.